Actuator

ABSTRACT

A self-contained actuator of the hydraulic type for moving loads of a magnitude and for distances not practical for electric solenoids. A fluid reservoir, an electric motor, a pump and a hydraulic cylinder are mounted on a common base to comprise a compact unit, together with a belt drive connecting the motor and pump, a check valve to hold the liquid in the cylinder, a solenoid-operated return valve to drain the cylinder and a metering valve to control the rate of flow out of the cylinder. A remote, manually controlled switch device is designed to energize the motor and the solenoid in a mutually exclusive manner, the switch device having a neutral position and a spring-operated cam for normally urging the switch device to its neutral position.

United States Patent Logan 1541 ACTUATOR [72] Inventor: Henry H. Logan, 6107 North Newbury Avenue,-Chicago, Ill. 60631 [22] Filed: Jan. 28, 1971 [21] Appl.No.: 110,509

[52] US. Cl. ..60/52 US, 60/DlG. 2, 60/52 R, 60/52 CD [51] Int. Cl ..Fl5b 15/18 [58] Field of Search.60/52 US, 52 T, 52 CD, DIG. 2, 60/52 HA, 52 P]; 92/85, 182, 201

[56] References Cited UNITED STATES PATENTS 1,427,241 8/1922 Sunderman ..60/52 HA 2,193,125 3/1940 Evans et al. ..60/52 T UX 2,280,291 4/1942 .laseph ..60/52 l-lD X 2,399,294 4/1946 Ray ..60/52 T 2,838,910 6/1958 Bacchi ..60/52 P] 51 Oct. 17, 1972 Primary Examiner-Edgar W. Geoghegan Attorney-Davis, Lucas, Brewer & Brugman [5 7] ABSTRACT A self-contained actuator of the hydraulic type for moving loads of a magnitude and for distances not practical for electric solenoids. A fluid' reservoir, an electric motor, a pump and a hydraulic cylinder are mounted on a common base to comprise a compact unit, together with a belt drive connecting the motor and pump, a check valve to hold the liquid in the cylinder, a solenoid-operated return valve to drain the cylinder and a metering valve to control the rate of flow out of the cylinder. A remote, manually controlled switch device is designed to energize the motor and the solenoid in a mutually exclusive manner, the switch device having a neutral position and a spring operated cam for normally urging the switch device to its neutral position.

5 Claims, 11 Drawing; Figures PATENTEUnm I! 1912 SHEET 1 OF 3 MWa f mil xx: mttatrmraug m- ACTUATOR This invention relates to actuators for moving relatively heavy loads for short and variable distances.

It is frequently necessary to apply a load through a short distance to actuate or deactuate some mechanism such as a brake, clutch, control lever, oven door, or the like. Where the loads and distances are small, a solenoid may. be employed to perform this task, the solenoid being compact, readily available and easily and quickly controlled. When the loads become great, the size and cost of the solenoid become impractical, and other means must be resorted to to accomplish the same result. These other means usually employ fluid power in one fonn or another, and although they may be able to perform the essential on-off functions of a solenoid, they do not take advantage of the additional capabilities of fluid power to increase their versatility.

, One such fluid power substitute for a solenoid which is commercially available is sold under the trademark Thruster and comprises a small reservoir of oil in which is immersed the impeller of a pump driven by an electric motor. The output of the pump is conducted to a hydraulic piston which is connected to an external yoke on which is a lug adapted to be connected to the load to be moved. The operation of the device is substantially identical to that of a solenoid except that its speed is considerably less. As long as the motor is energized, the yoke and lug will remain extended, but as soon as the motor stops, the yoke and lug are retracted by gravity. It is all on or all off, and it uses electricity as long as it is on.

The principal object of this invention is to provide an actuator for loads and distances which are greater than can be conveniently handled by a solenoid, said actuator using fluid power and requiring little or no energy to remain actuated.

Another object of this invention is the provision of a self-contained actuator for large loads to be moved for relatively short distances, wherein said actuator uses fluid power derived from an electric motor to operate a hydraulic cylinder, and means for automatically stopping the electric motor while maintaining the piston of the cylinder at its operative, load-supporting position.

Among its more general objects, this invention has within its purview the provision of an actuator in package form which is simple to manufacture and service, which is sufficiently versatile to meet many different conditions without excessive engineering variables, and which is small and presentable in appearance.

A more specific object of this invention is the provision of means, operated by the piston of a hydraulic ac tuator, for stopping the flow of fluid behind the piston when the latter has reached the end of its operative stroke, with manually controlled means for trapping the fluid behind said piston so that no power is required to hold the piston in its operative position.

These and other objects of this invention will become apparent from the following detailed description when taken together with the accompanying drawings in which: 1

FIG. 1 is a front elevational view of the actuator with its housing removed, and with portions of the actuator shown in section;

FIG. 2 is a rear elevational view of the actuator of FIG. 1, also with its housing removed and with portions of the actuator shown in section;

FIG. 3 is a rear elevational view, on an enlarged scale with respect to the actuator of FIG. 1, of a manual control for the actuator, the control having its cover removed and the view being taken along line 3-3 of FIG. 4;

FIG. 4 is a side elevational view of the manual control of FIG. 3;

FIGS. 5 and 6 are alternative schematic wiring diagrams for the actuator and manual control therefor;

FIG. 7 is an elevational view in section, on an enlarged scale, of the cylinder, piston and the apparatus immediately connected therewith;

FIG. 8 is a schematic wiring diagram of the automatic shut-off for the power source;

FIG. 9 is a schematic diagram of the hydraulic circuit for the actuator;

FIG. 10 is a small-scale view showing an example of the actuator in use; and

FIG. 11 is a schematic diagram of a modification of the circuit of FIG. 5.

By way of general description, the hydraulic actuator of this invention is comprised of a hollow base containing a liquid such as oil, a compact positive displacement-type pump such as a gear pump, an electric motor for driving the gear pump through a belt drive, a vertically disposed cylinder connected to the output of the pump, a piston in the cylinder directly connected to a ram which engages the load to be moved, a solenoid valve and a metering valve in the exhaust from the cylinder, a check valve in the input to the cylinder, and a manually operated remote control for the motor and solenoid valve. The control is comprised of a pair of spaced microswitches mounted in a housing, and a pivoted lever movable between them, the lever being adapted to operate one or the other of the switches. One switch energizes the motor and the other energizes the solenoid valve. The switches are mutually exclusively operable so that one or the other, but not both, can be operated at any one time. The mounting of the components of the actuator on the base is such as to result in a small self-contained unit.

Referring now to the drawings for a detailed description of the invention, and particularly to the schematic diagram of FIG. 9 showing the hydraulic circuit, the hydraulic actuator of this invention is comprised of a base 20 which is hollow and constitutes the reservoir for oil or other liquid medium 21 to be used in the lifting of the load. An intake pipe 22 is provided, said pipe having its open end disposed close to the bottom of the reservoir to avoid picking up any :air in the base 20. Intake pipe 22 is connected to a gear pump 23 the output of which is connected to a check valve 24 from which the oil as pressurized by pump 23 is conducted to the base 25 of a single acting cylinder 26 the axis of which may, for convenience, be disposed in a vertical direction. The piston in the cylinder 26, hereinafter to be described, operates a ram 27 which contacts directly, or through any suitable power transmitting device, a load designated generally by the reference character 28.

The exhaust from cylinder 26 is conducted through a pipe 29 to a solenoid-operated valve 30 and thence through a metering valve 31 to the return pipe 32 which conducts the oil to the bottom of the reservoir to make certain that the opposite end of the return pipe is always immersed in the oil and thus to insure an absence of bubbles or frothing in the oil.

The various elements of the actuator are compactly assembled together as shown in FIGS. 1 and 2, to which reference is now made.

In the form selected to illustrate this invention, base 20 is a substantially rectangular open-topped container over which is fastened a cover 33. To said cover 33 are secured the base 25 of the cylinder 26, a motor 34 by which gear pump 23 is driven, and a pump carrier 35 which is an inverted U-shaped casting straddling motor 34 and formed with a flat platform 36 to which pump 23 is secured. It is understood that cover 33 is provided with appropriate openings through which extend the intake pipe 22, exhaust pipe 29 and also a vent pipe 37 through which air may be drawn as cylinder 26 is filled with oil from the supply in base 20.

It is contemplated that the components of the present hydraulic actuator will be concealed or shielded, and to that end an upper plate 38 is provided, said plate having the same outline as the cover 33 so that a sheet metal housing, shown in dotted outline at 39, may be appropriately secured between plate 38 and cover 33. Plate 38 is supported at one end from base 33 by a pair of spaced rods 99 and at the other end by a flange 100 on cylinder 26.

It is contemplated that motor 34 will drive gear pump 23 through a belt drive 40 and that the speed of the pump relative to the speed of motor 34 will be selected to provide a predetermined rate of movement of ram 27. For an accurate control of pump speed, belt 40 may be of the toothed type, and the sheaves may be toothed to accept such belt. It is contemplated further that, depending upon the ultimate use to which the hydraulic actuator will be put, the rate of movement of ram 27 may be changed and accordingly, it is contemplated that different sizes of sheaves will be used on gear pump 23 to provide such differing rates of movement. To accommodate larger sheaves, plate 38 is formed with a dome 41 into which the larger sheaves may extend.

Referring now to FIG. 7, the cylinder 26 and its base 25 are shown in cross section, it being apparent that base 25 has an inlet opening 42 and an annular well 43 to receive the incoming oil from the check valve 24 and pump 23. Cylinder 26 is provided with a liner 44, preferably of an aluminum alloy, the interior surface of which is extremely smooth and with which a piston 45 cooperates. Said piston 45 is sealed with respect to the smooth inner wall of liner 44 by one or more piston rings 46 preferably made in a well-known manner from reinforced plastic material having a V-shaped radial cross section facing the pressure and forming thin pressure-sensitive annular lips engaging the liner wall to assure the retention of fluid under pressure on the lower side of piston 45. The piston rings 46 are spaced inwardly from the lower end of piston 45 to leave a land 99, the function of which will be described hereinafter.

Piston 45 may be formed integrally with a cylindrical ram 47 which extends upwardly through liner 44 and through a flanged guide 48 secured to the top of cylinder 26. Said guide 48 has a bushing 49 in contact with ram 47, said bushing being preferably made of a material adapted to absorb oil to provide lubrication for the movement of ram 47 therein. The lower portion of guide 48 is slightly larger than the diameter of ram 47 to provide clearance 50 therebetween through which air and any oil leaking past piston 45 may pass to a bleed outlet 51 which may be connected to a separate pipe such as 52 (FIG. 2) emptying into the base 20. The upper end of guide 48 is closed with a cap 53 appropriately sealed with respect to ram 47 to prevent both the entry of dirt from ram 47 into bushing 49 and the loss of oil from bushing 49.

The upper end 54 of ram 47 is of reduced diameter to provide a shoulder against which a member such as clevis 55 connected to the load may bear, said clevis preferably being secured to said upper end 54 by a set screw 56 operating in a groove 57 in said upper end 54.

It is contemplated that a safety feature will be incorporated in the control for the motor 34 by which gear pump 23 is driven so that when piston 45 reaches the upper end of its stroke, motor 34 will be automatically disconnected and hence will discontinue driving pump 23 and prevent an unnecessary buildup of pressure under piston 45 and its seal rings 46. Said safety device is comprised of a pin 58 disposed in cylinder 26 concentrically with piston 45 and ram 47, said piston and ram being formed with a recess 59 for this purpose. Said recess 59 has a counterbore 60 therein in which is secured by any appropriate means such as threads or the like a plate 61 formed with a central opening through which pin 58 extends and with side openings 62 communicating with recess 59. The upper end of pin 58 is provided with a head 63 which is adapted to be contacted by plate 61 just prior to piston 45 reaching the uppermost end of its stroke. The lower end of pin 58 has a spool 64 secured thereto in which rides the yoke 65 of a rocker arm 66 (FIG. 8) mounted on the under side of cylinder base 25. The other end of rocker arm 66 operates a plunger 67 on the end of which is a switch 69 adapted to make or break a circuit leading to motor 34 from a power line 70.

The operation of the safety device as just described is such that with plunger 47 in the position shown in FIG. 7, pin 58 will be urged continuously downwardly by a compression spring 71, preferably located between base 25 and spool 64, in which position plunger 67 is urged upwardly as viewed in FIG. 8 to complete the circuit to motor 34 through switch 69. When, however, plunger 47 nears the upper end of its stroke, head 63 on pin 58 will be contacted by plate 61, and, for the remaining movement upward of ram 47, will be lifted with plate 61. This causes rocker arm 66 to pull downwardly on plunger 67 and thereby open switch 69 and the line to motor 34, thus automatically stopping motor 34 when ram 47 reaches the upper limit of its stroke.

There are several ways in which the actuator of this invention may be operated. In general, however, the upward movement of ram 47 will be effected by energizing motor 34 so that it will drive pump 23 and force oil under pressure from base 20 through check valve 24 into cylinder 26 under piston 45. The height to which ram 47 is raised depends entirely upon how long motor 34 operates. Means therefor are provided for manually operating a switch which controls the current to motor 34 so that said switch may be opened at any time to stop the ram in any desired position. If, however, the manual control is not operated before ram 47 reaches its upper limit of movement the safety device represented by pin 58, rocker arm 66 and switch 69 will automatically come into play to stop motor 34. At any selected position of ram 47, leakage of oil under pressure from below piston 45 will be prevented by check valve 24 and solenoid valve 30. Inasmuch as the piston rings 46 are sensitive to pressure and will increase in sealing ability as the pressure increases, the downward movement of ram 47 will be prevented by the retention of the oil under piston 45. At the upper end of the stroke, that is, at the point where the safety pin 58 comes into play, should a leak occur past piston 45 so that said piston and the ram 47 slowly descend into cylinder 26, the descent of the piston will permit pin 58 to descend likewise, thereby operating rocker arm 66 in a manner to push plunger 67 upward as viewed in FIG. 8 and thus engage switch 69 to start up motor 34 to supply makeup oil to the cylinder.

To lower plunger 47 it is necessary to exhaust the oil from under piston 45. This is accomplished by solenoid valve 30. Said valve 30 is controlled by a switch, hereinafter to be described, which may be operated in a manner to open the valve and allow the oil to leave cylinder 26, thus permitting piston 45 to descend therein. The rate of descent is controlled by metering valve 31 which may be of any well known construction and preset for the flow therethrough desired. By increasing the restriction of valve 31 the descent of piston 45 in cylinder 26 is slowed down and the opposite effect is created by increasing the flow through valve 31.

The manual control for the switches controlling the operation of motor 34 and solenoid valve 30 is shown in FIGS. 3-6 inclusive, to which reference is now made.

The manual control may be remotely located with respect to the actuator of this invention and connected thereto by an appropriate cable. Said manual control may comprise a housing 72 in which is disposed a switch actuating lever 73 secured to a shaft 74 passing through a boss 75 on the exterior of housing 72 and fastened at its outer end to a manually operated lever 76. Within housing 72 are disposed a pair of microswitches 77, 78 of any well known rugged make, said micro-switches having external buttons 79 and 80, respectively, by which the switches are operated. Said buttons 79 and 80 are adapted to be contacted by appropriate bosses on switch actuating lever 73. To prevent damage to the switches 77 and 78 by excessive movement of buttons 79 and 80, appropriate adjustable stops 81 and 82 are provided in housing 72 in the path of movement of lever 73.

It is contemplated that one of the micro-switches will be used to control motor 34 and the other will be used to control solenoid valve 30. For purposes of illustration, it will be assumed that switch 77 controls solenoid 83 of the solenoid valve 30 and switch 78 controls motor 34. A typical circuit to effectuate such operation is shown in FIG. 5. In this circuit it is assumed that solenoid valve 30 will be of the normally open type and that the energization of its solenoid 83 will cause it to close. Thus, a line switch, shown schematically at 84, will normally be open when the actuator is not being used and hence solenoid 83 will not draw any current under these circumstances. When the actuator is to be used, line switch 84 is closed and micro-switch 79 is connected to be normally closed. It is contemplated that the micro-switch 79 will be of a commercially available type in which, by an appropriate selection of terminals,

the switch may be operated either as a normally open or a normally closed switch. In the circuit illustrated in FIG. 5, the normally closed arrangement is used. Switch 78 will be normally open and the circuit between line switch 84 and motor 34 as well as solenoid 83 will be as shown in FIG. 5.

To avoid the necessity of having the operator physically hold or select a neutral position between switches 78 and 79 in which neither one is operated, a spring return mechanism, shown in FIG. 3, is used. Said mechanism is comprised of a roller 85 mounted on the opposite end of lever 73 from shaft 74 and contacting a V-shaped notch 86 in a lever 87 pivoted at 88 in housing 72 and held against roller 85 by a tension spring 89. Thus, it may be apparent from FIG. 3 that lever 87 and roller 85 will tend to hold the manually operated lever 76 in a vertical position in which neither switch 78 nor switch 79 is operated.

In the arrangement shown in FIG. 5, to raise plunger 47, lever 76 is turned to the right in that Figure to operate switch 78 and thereby establish the circuit through safety switch 69 and motor 34. This starts the motor turning and causes pump 23 to pump oil under pressure from tank 20 into cylinder 26. As long as manually operated lever 76 is held against switch 78 to maintain said switch in closed condition, motor 34 will continue to run and cause pump 23 to force oil under pressure under piston 45. If ram 47 is to be stopped prior to its upper limit of movement, lever 76 is released and the automatic spring return 85-89 will restore the lever 76 to its neutral position. Should the lever 76 be held against switch 78 after plunger 47 reaches the top of its stroke, safety switch 69 will automatically be operated and will break the circuit to motor 34 to stop the motor and prevent an excessive build up of pressure in the hydraulic circuit to piston 45. This will also avoid a waste of power through an operation of motor 34 when the latter is not needed.

To lower ram 47, manually operated lever 76 is moved to the left as viewed in FIG. 5 to operate switch 79 and since the latter is a normally closed switch, its operation will result in an opening of the circuit therethrough thereby deenergizing solenoid 83 of solenoid valve 30 to open said normally closed valve and allow the oil under pressure to leave cylinder 26 through an exhaust opening 90 shown more clearly in FIG. 7. The lowering of piston 45 and ram 47 can be stopped at any time merely by releasing lever 76 to allow it to assume its neutral position and thereby allow switch 79 to close to complete the circuit through solenoid 83 and thus close valve 30.

Should a solenoid valve 30 be used in which the solenoid is energized to open the valve then it would be necessary to use the circuit shown in FIG. 6 to open the valve to allow the oil to leave cylinder 26. Those contacts of the micro-switch of FIG. 3 would be selected which provide for a normally open switch as shown at 79 in FIG. 6. In other respects the operation of the manually operated lever 76 would be identical, that is to say, it would be moved to the right as viewed in FIG. 6 to raise the plunger and it would. be moved to the left to lower the plunger.

The end of the downward movement of piston 45 is cushioned by locating the outlet opening 90 above the lowennost position of piston 45 in cylinder 26 as shown in FIG. 7. This causes land 99 of piston 45 to pass over and progressively restrict opening 90 at the end of the downward movement of piston 45 and results in a holding back of the piston 45. The pressure sensitive piston rings 46 do not pass over opening 90 and hence are not cut or otherwise damaged thereby.

As stated previously, the actuator of this invention may be employed in many different ways to perform work at a distance. One of such ways is shown in FIG. wherein the actuator is used to raise or lower a gate 91 such as a furnace door, or the like. The clevis 55 is shown connected to a lever 92 one end 93 of which is pivoted to a fixed point in the furnace room and the other end 94 is connected by a link 95 to the gate 91.

It may be observed in FIG. 10 that the geometry of the links 92 and 95 requires that the actuator changes its direction as lever 92 is pivoted. This change in direction is readily effected by mounting the actuator on a pivot 96 disposed on an axis which intersects the axis of plunger 47, said pivot 96 being mounted on a fixed plate 97. A resilient support 98 is provided between base and fixed plate 97 to counterbalance the unbalanced center of gravity resulting from placing the pivot 96 in line with the axis of plunger 47.

The gate-opening function illustrated in FIG. 10 is one which may well be performed automatically at the beginning and end of an automatically timed heating cycle. Under such conditions, gate 91 is designed to open fully and close completely, without any intermediate degrees of opening or closing. This makes unnecessary the use of the manual control of FIGS. 3 and 4, said control being replaced by an automatically operated off-on switch in the manner illustrated in FIG. 11. In that FIG. switch 99 is operated by a timer, thermostat or other automatic device, and the valve 30 controlled by solenoid 83 may be normally open so that should power fail, the valve will open and allow the plunger 27 to descend, thereby closing door 91 and confining the heat to the interior of the oven.

The circuit shown in FIG. 11 may also be used with a spring-operated brake (not shown) of a mine hoist. In such application, it is intended that should a power failure occur, the brake will be automatically applied. With a normally open valve 30, and with plunger 27 connected to oppose the brake spring, solenoid 83 will be deenergized upon a power failure, valve 30 will open and plunger 27 will be retracted thus allowing the spring-operated brake to be applied.

Thus the actuator of this invention can be used as an off-on device in the same manner as a solenoid. The type of valve used, i.e., whether normally closed or normally open depends upon the specific function the actuator is to perform and the safety requirements of that function.

It is understood that the gate-opening function illustrated in FIG. 10 is but one of many functions that the actuator of the present invention is capable of performing and that said function is not intended to be a limitation on the scope thereof. By way of example, the present actuator may also be used to operate the gate of a large valve, to pull the cable control for a remote device, etc.

It is understood further that other arrangements of the parts of the actuator are possible without departing from the scope of this invention. For example, the

motor and pump may be turned from the position shown in FIGS. 1 and 2 so that the sheaves and belt are outside and more readily accessible than when disposed between cylinder 26 and the motor and pump. Also the motor may be placed above the pump to shorten some of the piping connecting the pump to the check valve and the check valve to cylinder 46. The foregoing description therefore is merely illustrative of the preferred form of the invention and the scope of the invention is not to be limited thereto, but is to be determined by the appended claims.

I claim:

1. A unitary hydraulic actuator comprising a base, an electric motor mounted on said base, an oil reservoir movable with said base, a cylinder mounted on said base with its axis perpendicular to the plane of said base and in spaced relation to said motor, a pump, means supporting said pump and motor in superposed relation to one another from said base, speed changing power transmission means connecting the motor to the pump to drive the pump from said motor, a ram in said cylinder, a piston in said cylinder connected to said ram, inlet conduit means connecting the output of the pump to the lower end of said cylinder, outlet conduit means connecting the lower end of said cylinder to the oil reservoir, a check valve in the inlet conduit means between the outlet of the pump and the cylinder, an adjustable metering valve and a solenoid operated valve in series in the outlet conduit means, a source of electric power, manually controlled switch means for mutually exclusively connecting the motor and solenoid of the solenoid operated valve to the electric power source whereby to raise or lower the ram at will, and switch means operated by the piston for automatically disconnecting the motor from the electric power source when the piston reaches the end of its power stroke.

2. A hydraulic actuator as described in claim 1, said base being hollow and forming said reservoir and said means supporting the pump and motor from said base in superposed relation comprising a carrier secured at its lower end to the base adjacent the motor and having an offset at the other end extending over said motor and supporting the pump.

3. A unitary hydraulic actuator as described in claim 1, said base comprising a cover for said reservoir, a plate of substantially the same contour as the base disposed over said pump, means for supporting said plate from said base, and a housing bridging said cover and plate and extending therearound.

4. A unitary hydraulic actuator as described in claim 3, an individual housing for said manually controlled switch means and means in the switch means housing and operable upon said switch means constantly to urge said switch means to disconnect the motor from said power source and to condition said solenoid for valve-closing operation.

5. A unitary hydraulic actuator as described in claim 1, said switch means operated by the piston comprising a rod, said ram and piston having a recess to receive said rod in telescoping relation therewith, a stop in said recess engageable by the rod to limit relative movement between said rod and piston, a switch in series with said motor, and means connecting said rod to said switch to operate said switch by said rod to disconnect the motor from the source of electric power when the piston reaches the end of its power stroke and to connect the motor to the source of electric power when the piston retracts from the end of its power stroke.

a: a: a: t 

1. A unitary hydraulic actuator comprising a base, an electric motor mounted on said base, an oil reservoir movable with said base, a cylinder mounted on said base with its axis perpendicular to the plane of said base and in spaced relation to said motor, a pump, means supporting said pump and motor in superposed relation to one another from said base, speed changing power transmission means connecting the motor to the pump to drive the pump from said motor, a ram in said cylinder, a piston in said cylinder connected to said ram, inlet conduit means connecting the output of the pump to the lower end of said cylinder, outlet conduit means connecting the lower end of said cylinder to the oil reservoir, a check valve in the inlet conduit means between the outlet of the pump and the cylinder, an adjustable metering valve and a solenoid operated valve in series in the outlet conduit means, a source of electric power, manually controlled switch means for mutually exclusively connecting the motor and solenoid of the solenoid operated valve to the electric power source whereby to raise or lower the ram at will, and switch means operated by the piston for automatically disconnecting the motor from the electric power source when the piston reaches the end of its power stroke.
 2. A hydraulic actuator as described in claim 1, said base being hollow and forming said reservoir and said means supporting the pump and motor from said base in superposed relation comprising a carrier secured at its lower end to the base adjacent the motor and having an offset at the other end extending over said motor and supporting the pump.
 3. A unitary hydraulic actuator as described in claim 1, said base comprising a cover for said reservoir, a plate of substantially the same contour as the base disposed over said pump, means for supporting said plate from said base, and a housing bridging said cover and plate and extending therearound.
 4. A unitary hydraulic actuator as described in claim 3, an individual housing for said manually controlled switch means and means in the switch means housing and operable upon said switch means constantly to urge said switch means to disconnect the motor from said power sourCe and to condition said solenoid for valve-closing operation.
 5. A unitary hydraulic actuator as described in claim 1, said switch means operated by the piston comprising a rod, said ram and piston having a recess to receive said rod in telescoping relation therewith, a stop in said recess engageable by the rod to limit relative movement between said rod and piston, a switch in series with said motor, and means connecting said rod to said switch to operate said switch by said rod to disconnect the motor from the source of electric power when the piston reaches the end of its power stroke and to connect the motor to the source of electric power when the piston retracts from the end of its power stroke. 